docs: def html5_serialize_simple_color(simple_color):
      """
      Apply the serialization algorithm for a simple color from section
      2.4.6 of HTML5.
  
      """
      red, green, blue = simple_color
  
      # 1. Let result be a string consisting of a single "#" (U+0023)
      #    character.
      result = u'#'
  
      # 2. Convert the red, green, and blue components in turn to
      #    two-digit hexadecimal numbers using lowercase ASCII hex
      #    digits, zero-padding if necessary, and append these numbers
      #    to result, in the order red, green, blue.
      format_string = '{:02x}'
      result += format_string.format(red)
      result += format_string.format(green)
      result += format_string.format(blue)
  
      # 3. Return result, which will be a valid lowercase simple color.
      return result